Scaled Crash Testing Using Modeling, Similitude, and Experimentation

Abstract

Due to the complexity and challenging nature of predicting the effects of impact on a vehicle, much of the crash-testing industry remains one which operates at full-scale. Automobiles and even aircraft are often crashed at full size, which is an expensive and time-consuming process. This paper details a novel approach to crash-testing that combines early use of simulation, scaling of the appropriate parameters using similitude, and limited testing. The method was used to predict the crashworthiness of a small, commercial unmanned aerial vehicle (UAV). The authors were involved in an undergraduate design project to develop a system capable of safely decelerating the RQ-7 Shadow Unmanned Aerial System (UAS) from an operational flight without the use of a runway. For contingency reasons or tactical purposes, the use of a larger runway for the UAS was not feasible. The team developed an airbag-like system that used controlled release of air to decelerate the vehicle. However, due to testing constraints the team was unable to test the airbag system at full-scale with an actual RQ-7 vehicle. The system is already far in it’s life-cycle so there were no prototypes available and the team’s available facilities would not facilitate a large, high-speed test. As a result, the team built a model of the existing vehicle, focusing on key components and materials. The team then conducted testing at both geometric and dynamic scale and used the results of those tests to determine if actual loading would potentially damage the vehicle. The paper demonstrates the utility of such an approach using the RQ-7 case study. Key aspects of the approach were the use of a model of the vehicle to determine the likely loading conditions that would lead to material failure. An analysis of the important scaling characteristics was conducted and a novel, non-dimensional ratio was developed. Scaled testing was conducted using instrumentation to determine the unknown scaling parameters. The results were then compared to the actual vehicle through the use of the non-dimensional ratio. The ratio compared the size, the approach speed, and the mass of the model to the actual air vehicle with the ultimate goal of determining whether the decelerations experienced by the model when impacting the airbag, would result in damage to key components on the vehicle when decelerated at full-scale. Testing showed that the model airbag was capable of adequately decelerating the UAV, although improvements needed to be made for greater reliability.